Basic M2 Sigma Drive wiring error damaging?

I just picked up a Kenwood Basic M2 in good condition for what I would consider a good price.

The seller gave me the required demo on his kitchen table, prior to which he had connected the speakers incorrectly.

He had one speaker wired to the A channel + and -.

He had the other wired to the A channel sigma drive sensor + and -.

When he turned things on and fed a signal to the amp, this error caused a substantial hum to leap forth from said speakers.

This in turn caused my teeth to clench shut and my eye brows to raise higher than my forehead should permit.

He quickly proceeded to shut things down and correct the wiring error.

The amp then produced the expected sweet sounds.

My question is....should I be concerned that this screw-up by the seller will cause me grief in the near future or lessen the life of this nice piece of kit?

Or....would the common opinion be that I dodged a bullet.

Or perhaps it's no big deal at all?

Anyone?

It should be perfectly fine, as long as he didn't short the speakers. The original M1 had this issue as well if you wired to the feedback terminals. Lots of noise. The terminals there to monitor the back EMF voltages.